C# 如何在数据列表中进行文件上载？

这是数据列表：

protected void DataList1_ItemCommand(object source, DataListCommandEventArgs e)
{
    FileUpload file = (FileUpload)DataList1.FindControl("FileUpload1");
    file.SaveAs(Request.MapPath("//") + "resume//");
}

单击该按钮时出现错误：对象引用未设置为对象的实例。请将数据列表张贴在此处。另外，您希望何时启动此事件？

<asp:DataList ID="DataList1" runat="server" OnSelectedIndexChanged="DataList1_SelectedIndexChanged" OnItemCommand="DataList1_ItemCommand">
    <ItemTemplate>
            <div class="jumbotron">
                <div class="card-primary">
                        <asp:LinkButton ID="job_pos" runat="server" Font-Size="XX-Large"><%#Eval ("JobPosition") %></asp:LinkButton>
                        <h4 style="font-weight: bolder"><%#Eval ("CompanyName") %> <span class="icon"><i class="fa fa-building"></i></span></h4>
                        <h5 style="font-weight: bold; color: #808080"><%#Eval ("Region") %> <span class="icon"><i class="fa fa-map-marker"></i></span></h5>
                        <h5 style="font-weight: bold; color: #808080"><%#Eval ("ExactAddress") %></h5>
                    <div>
                        <h5><%#Eval ("JobDesc") %></h5>
                        <div>
                            <asp:Label ID="Label2" runat="server" Text="Interested? Apply Now!" Font-Bold="True" ForeColor="Red"></asp:Label>
                            <asp:FileUpload ID="FileUpload1" runat="server" CssClass="primary"/>
                            <asp:Button ID="Button1" runat="server" Text="Upload Resume" OnClick="Button1_Click" CssClass="btn-primary" CommandName="UPDATE"/>
                        </div>
                    </div>
                </div>
            </div>
    </ItemTemplate>
</asp:DataList>